This probably has been asked many times before (I think I may have even asked it once---can't find my old post, though, & can't remember the answer): Has IFing been found to decrease the metabolism over time? For instance, let's say that I regularly skip breakfast and eat only between 2 - 7 p.m. Have there been any studies that show that doing something like that consistently would damage the metabolism? Just curious.

@lin43 Everything I have researched on the subject says metabolism slowdown due to dieting is a myth, although some will insist it exists. One of my favorite blogs is Mark's Daily Apple. He says there is no credible evidence the metabolism slows down or is "damaged" by skipping meals or low calorie diets. The one exception is a starvation type diet, but even in this case it takes weeks for the metabolism to slow down, and rebounds quickly when eating is resumed. It is true we need less calories the more weight we lose, but this isn't really a metabolism issue, just that there is less weight to move around and less fuel needed for that movement. Mark says intermittent fasting actually revs up the metabolism, because during brief periods of fasting, the body becomes more efficient at burning it's own fat stores.

I've decided that I'm going to do South Beach along with 8/16. Calories definitely count, you guys are so right, but I definitely don't want to count them. So I think this will be a great combination for me.

Re counting calories for coffee...On the Leangains website, less than 50 calories is recommended; in the 8 Hour Diet Book, 40 calories is recommended; they won't break the fast.

Personally, I like my coffee black, but I do drink a Fuze Slenderize in the morning (15 calories) to ward off hunger. It contains Citrimax and really works!

Thank you!

Actually Bigsky is partially wrong.

Your metabolism doesn't slow down between meals - and short term fasting won't slow down your metabolism. Actually, the bodies first reaction to no food is to speed up one's metabolism. Therefore - metabolism is unaffected by the number of meals one eats in a day.

Where Bigsky is wrong (and I'm sure Mark didn't say what Bigsky thinks) is that when you're dieting your body does slow down your metabolism. You don't need to be on a starvation diet. You reduce calories and your body will adapt. How much and how fast this happens depends but at most it seems to be around 10% -15% of BMR.

This is fairly well documented. It's also fairly well documented that when you start eating again your metabolic rate will return to normal. There are very few cases where you can permanently damage your metabolism. Even in the Minnesota starvation study after six months metabolisms had returned almost 100% to normal. (Once you factor in the differnce in body size)

Bigsky I think if you go back and look at what Mark did and didn't say you'll see you misread. I doubt he would have made such an error.

The "rule of thumb" is to stay under 50 calories in order to not "break the fast."

Thanks. That's reassuring. It makes me want to give IF another shot as a maintenance plan (I've tried it briefly in the past).

Oh yes - I missed this question. This is another one of those no one knows questions. No one knows because -

If you're worried about fat loss only it makes no difference

If you're worried about the "health benefits" no one knows what those are for humans, how long one must fast or what level of calories would break it.

The 50 calories number came from Martin Berkham who just pulled 50 calories out of his bottom as far as I can tell. It is more of a compliance issue - meaning - people are more likely to stick with his plan if they can have a little cream in their coffee. Also, 10g of BCAA he suggest has calories.

Personally - I keep it under 25 calories. Why? No idea.

@lin43 I went back to find the information on metabolism and dieting...actually the source was not Mark's daily Apple at all. My error. It was a blog called "Fatty Fights Back:Mythbusters. A very interesting although lengthy article on the starvation mode myth. It was that which I was referring to when I tried to answer your question. The idea that the body goes into "starvation mode" and prevents further weight loss. There are many articles, not so much on I.F., but on reduced calorie dieting and the supposed starvation mode, and that it isn't really true.

Yea - starvation mode is a myth. The body has energy needs and they will be met. The idea that the body will hold onto everything we eat because it's starving is ignorant. (Yet repeated constantly around the web)

Thanks, BigSky. I'll have to check out that blog.



I figured it was bogus, but what throws me off is the research that suggests that the formerly overweight/obese who lose weight often cannot eat as many calories to maintain as someone of comparable size who was never overweight. That led me to speculate that it might have something to do with the prolonged restriction of calories.

Hi all,


Just wondering if this IF plan will work if I have a long schedule? 5AM TO 9PM daily including work and gym. I usually don't sleep until 11PM either... most sleep I've gotten since forever lately.

It has little to do with metaboilsm and more to do with motion. NEAT and SPA are measurably different in those who have lost weight than those who have never lost weight. Whether this is an adaptation or not is unknown.

I can't seem to go shorter than an 8 hour window. I have tried a 5 hour window but it was really hard and I always ended up eating past my time. Also, if I stop eating too early in the day, I get intense hunger pangs in the evening. So I basically do 12-8.
Why is it that I get extremely hungry about an hour after eating supper? No matter what I eat. I have tried adjusting my carbs, protein, etc but it makes no difference. Is it a blood sugar thing? Maybe leptin resistance? Anyone have any advice? Been doing I.F. for a over month now without much success.

Adjust what you are eating in your window BigSky to reduce your calorific intake. What I call, "doubling it up".

When I started eating massive salads I saw a big difference compared to eating just what I wanted like sandwiches or whatever. Think BIG portions of super-HEALTHY. And limit your carbs by avoiding bread, rice, potatoes, sugar etc.

Now, I keep my breakfast super light and try to control my salad portion size for lunch as well and that really has upped things.

Although I don't technically IF of course because of the beer, but had to suggest this.

You could, of course, also try a beer in the evening to blast those hunger pangs! Works a treat for me. But avoid the muchies. Get a good IPA. Or try a glass of red wine. Works just as well.